Research

EWG’s 2018 Guide to Bug Repellents : Repellent Chemicals

Picaridin

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Picaridin, developed by Bayer AG in the 1980s and sold in the U.S. since 2005, has very low inhalation toxicity, is not known to irritate skin, and does not have a pungent odor like DEET.1 It evaporates from the skin more slowly than DEET or IR3535, and may repel bugs for longer periods.2 A review of reports to the National Poison Data System between 2000 and 2015 found only one moderate effect reported from the use of picaridin-containing products – the remaining cases were classified as having minor impacts, including ocular irritation or pain, vomiting or oral irritation.3

In efficacy testing picaridin performs like DEET, appearing to repel a wide range of pests. A 2018 science review comparing the mosquito repellency of DEET with picaridin considered more than 140 field and laboratory studies and found no significant difference in performance.4 EPA registration data indicate that picaridin at a concentration of 20 percent is effective against mosquitoes and ticks for eight to 14 hours, and at a concentration of 10 percent it is effective for five to 12 hours.5

Picaridin does not carry the same neurotoxicity concerns as DEET, but has not been used as extensively by people. Overall, EWG’s assessment is that picaridin is a good alternative to DEET with many of the same advantages and without the same disadvantages.

DEET

DEET, registered for public use in 1957, is the most common mosquito and tick repellent. It is rated as very effective in repelling a wide range of mosquitoes, ticks and other bugs. DEET has been used billions of times and is a reasonable, if imperfect, choice.

In 1998, the EPA reviewed the first 40 years of public usage of DEET along with its known toxicity information, and concluded that “the normal use of DEET does not present a health concern to the general U.S. population.”6 And the agency found “no toxicologically significant effects in animal studies.”7

When EWG started our research, we were particularly concerned about the potential downsides of DEET. We still are. We urge consumers to handle DEET with caution. It is known to irritate the eyes and in intense doses it may induce neurological damage.8,9,10 In very rare cases, DEET has been reported to impair the nervous system, with symptoms including seizures, tremors and slurred speech – this most often occurs after exposure to high concentrations of the chemical.11,12 In addition, DEET gives off a distinct odor, and can damage plastic, rubber and vinyl on clothing, backpacks, glasses, watches and cameras.13,14

In 1998, after reviewing case reports of seizures, the EPA concluded that the rate of adverse reactions appeared to be very low – on the order of 1 per 100 million persons. The agency instructed manufacturers to provide additional instructions for minimizing overexposure to DEET. It authorized DEET for use by children, but banned marketing claims that DEET products are “safe for children.”15 The EPA said it had “no evidence that would lead [it] to believe that DEET is uniquely toxic to infants and/or children,” but it added that its personnel still had “concerns regarding these seizures, especially for children who are more susceptible to seizures in general and who receive a higher dose of DEET due to a greater surface area to body weight ratio.”16

Laboratory studies conducted since the 1998 EPA review have suggested that intense DEET exposure can affect the nervous systems of rats.17,18 People who use DEET daily have reported suffering symptoms including rashes, dizziness, difficulty concentrating and headaches.19

Still, after reviewing the evidence, EWG has concluded that DEET is generally safer than many people assume and remains a viable option for people in areas infested with disease-carrying pests. As rates of bug-borne illnesses rise, people need bug repellents that work well when it counts.

The EPA allows sales of repellents with up to 100 percent DEET, but increasing concentration does not increase efficacy. Longer protection times can be achieved by time-release products. We think it makes sense to follow Canadian government recommendations limiting DEET to 30 percent in any product, and using even weaker concentrations for young children.20 The Canadian government’s advice is more conservative than the CDC’s 2016 recommendation to use a product containing 20 to 50 percent DEET for adult protection against Lyme disease, and a product containing 20 to 30 percent DEET for children’s protection. Consumers must make their own decisions about which advice to follow when it comes to using DEET on children in areas with a high risk of Lyme disease.

Use only when bug risks are high
5-10% DEET
Limit to one application per day

2 to 12 years

5-10% DEET
Limit to three applications per day

Avoid prolonged use

General population

No more than 30% DEET allowed in products

IR3535

IR3535, whose full chemical name is 3-[N-Butyl-N-acetyl]-aminopropionic acid, ethyl ester, is structurally similar to the naturally occurring amino acid B-alanine. Merck & Co. developed IR3535 in the mid-1970s. It has been used in Europe for more than 20 years, but was not registered for use in the U.S. until 1999.22

IR3535 can be very irritating to the eyes, but poses few other safety risks. European authorities have received no reports of health problems caused by this chemical. Like DEET, IR3535 may dissolve or damage plastics. The manufacturer recommends avoiding contact with plastics other than polyethylene and polypropylene.

A comprehensive review of public efficacy studies completed between 2000 and 2013 found the performance of IR3535 to be similar or slightly less effective than DEET and picaridin against mosquitoes. Against deer ticks, IR3535 provided over twice the mean protection time of DEET, picaridin or Oil of Lemon Eucalyptus.

This chemical is most often found in products sold as sunscreens and repellents. We recommend avoiding these products because sunscreen should be reapplied every two hours, but following those instructions would overexpose the user to bug repellent.

In sum, IR3535 is a good all-around option that should provide strong mosquito repellency and good tick repellency.

Oil of Lemon Eucalyptus/PMD

Oil of Lemon Eucalyptus is the trade name for the repellent that originated as an extract of the eucalyptus tree native to Australia. The tree extract is refined to intensify the concentration of the naturally occurring substance para-menthane-3,8-diol, also known as PMD, from 1 to 65 percent. The resulting oil is very different from unprocessed tree oil.

Most Oil of Lemon Eucalyptus products on the market are made by Spectrum Brands and sold under the brand names Repel and Cutter. These have concentrations of 30 percent Oil of Lemon Eucalyptus and 20 percent PMD. Some testing has shown that concentrations of 20 to 26 percent PMD may perform as well as 15 to 20 percent DEET against both mosquitoes and ticks.24 The Oil of Lemon Eucalyptus active ingredient by itself, PMD, has a maximum protection time against mosquitoes and ticks that is shorter than DEET’s, with only two hours of protection according to EPA documents.

Refined Oil of Lemon Eucalyptus is classified as a biochemical pesticide, which the EPA defines as a naturally occurring ingredient that controls pests by nontoxic mechanisms. Ingredients in this category can qualify for EPA approval with less safety testing than synthetic chemical pesticides. However, unlike botanicals, these products must submit tests showing effectiveness.

Because the dangers to children have not been thoroughly explored, products with Oil of Lemon Eucalyptus and PMD have labels that warn, "Do not use on children under the age of 3."25 The CDC also advises not to use on children under 3 years of age.26 Citronellol and other chemicals in the extract are known allergens.

Synthetic PMD can be found in some repellent products at a concentration of 10 percent. These products provide only a few hours of protection and also warn against use on children younger than 3 years old. They present less risk of allergic skin reaction than natural PMD.

Scientists do not know enough to determine differences between PMD and Oil of Lemon Eucalyptus, but one study found that Oil of Lemon Eucalyptus provided longer protection than the equivalent concentration of synthetic PMD.

We conclude that Oil of Lemon Eucalyptus has disadvantages and is not appropriate for all situations, but is a good choice for people who want a botanically based bug repellent.

2-Undecanone, or methyl nonyl ketone, is an EPA-registered repellent that also can be found naturally in many plants such as cloves, strawberries and tomatoes. It was first registered with the EPA for use as a dog and cat repellent, and has been patented as a repellent for use against apex predators such as wolves, bears and tigers.27,28 In laboratory studies, the ingredient showed no toxicity via oral and inhalation routes, but it demonstrated slight dermal toxicity and caused some dermal and eye irritations. There is only one product registered with the EPA to use 2-undecanone. It is sold as Bite Blocker BioUD and is registered to provide five hours of mosquito repellence and two hours of tick protection. There are very few public studies comparing the efficacy of 2-undecanone with other repellents, although it is effective as DEET is some tests.29

Botanical repellents

EWG research indicates that unregistered, botanically based bug repellents are often not the best choice. The most common ones contain castor oil, cedar oil, citronella oil, clove oil, geraniol oil, lemongrass oil, peppermint oil, rosemary oil and/or soybean oil. While effectiveness varies, and there may be a few exceptions, most botanicals repel bugs for a short time, if at all.

There are few data available on botanicals because the EPA has classified them as "minimum risk" pesticides, meaning they are exempt from registration and efficacy testing. But "minimum risk" does not mean safe. Products based on these botanical ingredients generally contain known human allergens – often at much higher concentrations than personal care products.

EWG recommends that consumers who are in high-risk areas for bug-borne disease or who need long-lasting, effective bug protection avoid botanically based bug repellents, aside from Oil of Lemon Eucalyptus. In other cases, you may find it worth your while to try botanical repellents to identify one that works well for you. To determine if a product might cause an allergic reaction, EWG suggests testing it on a small patch of skin before slathering it all over.

Botanical oil

Likely to contain these known human allergens**

Castor oil

None

Cedar oil

None

Citronella oil

Geraniol*, citronellol*, limonene*, linalool*, farnesol*

Clove oil

Eugenol*

Oil of Lemon Eucalyptus (PMD 65%)

Citronellol, pinene, caryophyllene

Geraniol oil

Geraniol*, citronellol*, linalool*, limonene*

Lemongrass oil

Geraniol*, citral*, citronellol*, limonene*

Peppermint oil

Menthol, caryophyllene, limonene*, pinene

Rosemary oil

Pinene, camphor, caryophyllene, limonene*, terpineol, linalool*

Soybean oil

None

*In Europe, cosmetics applied to the skin must disclose these ingredients when the concentration exceeds 0.001 percent (SCCS 2003).
** Known human allergens identified by the European Commission Scientific Committee on Consumer Safety (SCCS 2011).

4 Larry Goodyer and Steven Schofield, Mosquito Repellents for the Traveller: Does Picaridin Provide Longer Protection than DEET? Journal of Travel Medicine, May 2018, 25:S10–S15. Available at doi.org/10.1093/jtm/tay005

8 Ali Abdel-Rahman et al., Subchronic Dermal Application of N,N-Diethyl m-Toluamide (DEET) and Permethrin to Adult Rats, Alone or in Combination, Causes Diffuse Neuronal Cell Death and Cytoskeletal Abnormalities in the Cerebral Cortex and the Hippocampus, and Purkinje Neuron Loss in the Cerebellum. Experimental Neurology, 2001, 172(1):153-171. Available at doi.org/10.1006/exnr.2001.7807

12 G. Briassoulis et al., Toxic Encephalopathy Associated with use of DEET Insect Repellents: A Case Analysis of its Toxicity in Children, January 2001, 20(1):8-14. Available at doi.org/10.1191/096032701676731093

17 Ali Abdel-Rahman et al., Subchronic Dermal Application of N,N-Diethyl m-Toluamide (DEET) and Permethrin to Adult Rats, Alone or in Combination, Causes Diffuse Neuronal Cell Death and Cytoskeletal Abnormalities in the Cerebral Cortex and the Hippocampus, and Purkinje Neuron Loss in the Cerebellum. Experimental Neurology, 2001, 172(1):153-171. Available at doi.org/10.1006/exnr.2001.7807

29 B.W. Bissinger et al., Comparative Efficacy of BioUD to Other Commercially Available Arthropod Repellents Against the Ticks Amblyomma americanum and Dermacentor variabilis on Cotton Cloth, American Journal of Tropical Medicine and Hygiene, October 2009, 81(4):685-690. Available at www.ncbi.nlm.nih.gov/pubmed/19815887